1. Field of the Invention
The present invention relates to an apparatus for forming a compound-semiconductor thin-film, which can form high-quality compound semiconductors using the cluster ion beam deposition method.
2. Description of the Prior Art
In addition to element semiconductors consisting of such elements as silicon or germanium, compound semiconductors consisting of two or more kinds of elements such as those of Groups II and VI or Groups III and V have been proposed recently and brought into practical use as light-emission diodes, semiconductor lasers, etc.
In the case of the compound semiconductor, the band gap may be optionally changed by varying the kinds of the component elements and composition thereof. Therefore, for instance, the light-emission diode mentioned above can be made to emit light of any desired wavelength in the region from red light to green light. In addition, the compound semiconductor is very large in the mobility of electrons, and therefore is finding practical applications in ultra high frequency devices, solid-state oscillation elements for microwave, laser oscillation elements, etc.
The above-mentioned compound semiconductor has been heretofore produced by making it grow epitaxially on a substrate by the use of the vapor or liquid growth process, and the like. However, the above production method of the compound semiconductor has the following disadvantages.
First, the component elements of the compound semiconductor are different in chemical and thermodynamic properties from one another. Therefore very complicated operations and processes are necessary to produce a desired product having a correct stoichiometric composition. For instance, in the case of the III-V compond semiconductor, its components of Group V such as phosphorus (P) and arsenic (As) are very high in vapor pressure though it is a high melting point compound. Therefore, in order to produce a semiconductor high in crystal quality, it is necessary to process phosphorus, arsenic, and so on in a high-pressure atmosphere, since otherwise the substances high in vapor pressure tend to escape as the temperature increases.
In addition, if the crystal quality is poor, the semiconductor tends to cleave along crystal grain boundaries and therefore requires a troublesome post-treatment.
Moreover, the compound semiconductor is composed of a plurality of component elements different in property. Therefore, the conventional method requires very complicated processes for the production of the compound semiconductors as mentioned above and as a result can hardly mass-produce the products. Thus the compound semiconductors produced become high in price.